Reproducibility of measures of leg muscle power, leg muscle strength, postural sway and mobility in people with Parkinson's disease

Muscle power, muscle strength and postural sway are considered to be determinants of fall risk and gait in Parkinson's disease (PD) and potential targets for therapeutic trials. However, the potential usefulness of these tests as outcome measures depends on their reproducibility in the PD population. Therefore, measures of leg muscle power, leg muscle strength, postural sway and mobility were taken on two occasions 1 week apart in 31 people with PD. Measures of muscle power, muscle strength and mobility were found to be very reliable (intraclass correlation coefficients (ICC3,1 0.50-0.97)) and showed good agreement, i.e. small measurement error. Postural sway measures showed poor reliability (ICC3,1 0.04-0.51) and agreement, especially in the presence of disabling dyskinesia. The moderate to high reproducibility of leg muscle power, muscle strength and mobility measures in people with PD confirm their suitability as outcomes measures in clinical and research settings. Further research into the clinical measurement of postural sway in people with PD is warranted, especially in individuals with dyskinesia.

► Leg muscle power and strength measures have high test-retest reliability in PD. ► Repeated sit-to-stand and TUG are highly reproducible and simple to use clinically. ► The reliability of postural sway measures is adversely influenced by dyskinesia.